Since the invention of underground sewer system over a century ago, engineers and inventors have been trying to solve the problems related to the manhole cover failure. These problems include: (1) manhole cover ring support failure (mortar); (2) inflow and infiltration (I/I) of storm and underground water into the manhole; (3) rising road surface due to the freeze/frost and heave action; (4) raising manhole cover due to resurfacing the road asphalt; and (5) challenges in practically adjusting the manhole cover according to the road slope.
Manhole cover failure is a significant financial burden on the municipalities. In order to have proper flow of traffic, it is necessary to re-level the manhole cover with the road. Since the municipalities' specification, in general, do not provide an engineered direction on how to adjust the manhole cover slope according to the road slope, many issues arise after the installation. The specifications do not provide proper means of levelling the manhole cover ring and its adjustment to the slope of the road. The specified mortar connection cannot be engineered to resist the AASHTO (American Association of State Highway and Transportation Officials) specified traffic load. In addition, the current mortar connection does not allow for proper design of the connection to stabilize manhole cover ring. Therefore, it naturally ends up failing under traffic load, as the grading rings rupture and fall apart causing the manhole ring to drop down and become a traffic hazard.
The manhole cover ring is usually placed on the top of the last manhole shaft piece (tapered section). Since the manhole shaft bottom is below the freeze and frost depth, the shaft is not subject to heave action. Therefore when the road surface is lifted up due to the winter heave the manhole cover does not rise with the road surface, since it is placed on top of the manhole shaft.
Since the waste water sewer is warm, and also the manhole shaft is not insulated at the freezing depth, the generated warm air penetrates through the manhole shaft wall to the immediate surrounding soil and the road base, causing the surrounding soil not to heave and not to rise with the road surface.
When the mortar holding the manhole cover ring fails, and the surrounding asphalt rises, the asphalt surrounding the manhole cover ruptures. Since the manhole shaft, which receives the manhole cover ring, is not water and air tight, it allows the water to flow toward a low point, namely the manhole. Water, eventually, finds a way to seepage toward the shaft, and on the way washes out the road base fine particles and loosens the road base. This expedites the manhole cover and surrounding asphalt failure.
Usually roads have two directional slopes, one slope (in general 2%) toward the side to carry the rain and storm water toward the curb and another slope longitudinally in the road direction, called uphill or downhill slope. In order for the manhole cover to be installed perfectly, it should be set according to the above two slopes. Otherwise the manhole cover will not match with the road surface, and the edges of the manhole ring will be either higher or lower than the road final level, which creates traffic issues.
The currently available systems to level the manhole cover with the road slope lack proper installation system at all stages of the road construction, including: at a new road construction; at resurfacing stage; during overlaying a new layer on the top of the old one; at the stage of repaving the existing failed manhole; during replacing of the top layer of asphalt; and when repairing the existing manhole cover.
The prior arts related to the manhole cover has tried to resolve some of the issues discussed above. However, none have been able to solve all issues. Most have tried to find a way to raise a manhole cover that has fallen below the road surface. The prior art has not addressed the issue that the manhole cover ring is fixed on the top of a manhole shaft which does not move, while the surrounding road material moves up and down due to the heave action. The prior art also discloses methods to level the manhole cover, and tries to stop the inflow and infiltration (I/I) to the sewer system through manhole.
The prior art, however, does not consider the complex interrelation between the heaving action, the road level and a fixed manhole shaft. The main issue of the prior arts is that they do not consider the heave action of the road surface, and that the road asphalt heaves around the poured concrete. In addition, its reinforcing is not properly engineered and does not include shear reinforcement. In addition, the prior art manhole covers do not provide the option of asphalt topping to match the asphalt finished road. And finally if the road is resurfaced the manhole cover ring cannot be raised since it is casted in the poured concrete. The self-leveling manhole covers perform self-levelling only during the installation process and ignore the heave effect of the road surface, which alters the original leveling after one season. Also these systems are practically very difficult to install.
In general, all of the prior arts have one major common character, namely that they place and fix the manhole cover ring on the manhole shaft top. Manhole shaft is a fixed point and when the road heaves the manhole cover, even if it does not fail, stays below the road level and becomes a pothole.
The present invention provides a floating manhole cover that moves with the heave action of the road. It is a sustainable and cost effective engineered solution that will eliminate regular manhole cover repairs, saving municipalities a significant amount of money. It also increases public safety by providing a better traffic flow and smoother road surface. It also reduces vehicle alignment damage and repair cost.